How to pin and unpin your screen on Android Oreo 8.0 & 8.1 phones

How to lock your screen to stay on a particular app
This can be useful if your child for example, is playing on your phone and you don't want them to be able to access other areas of your phone.
Steps:
To enable screen pinning, go to settings.
Scroll up look for security & Location and tap on it.
Scroll up and tap on Screen Pinning.
Turn on Screen Pinning and turn on the option "Ask for unlock Pattern before Unpinning".
Now to pin your screen first choose an app and tap on it, let's say Radio.
Now tap on the Square icon at the bottom of your screen and tap the pin icon that appears on the bottom right side of the App.
Now your screen is pinned on the Radio app.
As you can see you can't minimize or do anything else on your screen apart from using the app.
To unpin the screen, tap and hold the return and square icon at the same time.
Now your phone will ask you to enter the pattern or Pin you use on your phone.
Enter it and your screen will be unpinned.